The printing field is one of many fields of manufacturing and commercial activity in which coated materials are photochemically cured by means of high temperature curing systems. One such system makes use of ultra-violet radiation from medium pressure mercury vapor lamps, which, by their nature, operate at a temperature of between about 1100.degree. F. to 1400.degree. F. One of the most serious problems associated with such lamps is that the high operating temperatures rapidly dissipate heat to the surrounding areas and adjacent equipment. The ultra-violet lamps are mounted in reflector assemblies, and during normal operations the lamp reflector assemblies are cooled by air and/or water and, in many cases, air is circulated in and around such assemblies and adjacent equipment. The purpose of such cooling is to maintain the lamp reflector assemblies and adjacent equipment at reasonable operating temperatures, and to reduce the amount of heat that is transmitted to the coated substrates. While the cooling is reasonably effective for normal operations, any curtailment of operations, particularly one which interrupts the movement of the coated substrate, either for a short interval or long period, causes substrate temperatures to rise and creates a variety of problems.
One of the general operating parameters of medium pressure mercury vapor lamps is that they cannot cycle from an off-state mode to running power easily. This is due to the fact that such lamps must run at an operating temperature of between about 1100.degree. F. to 1400.degree. F. and whenever a lamp is shut down the mercury therein must be mostly recondensed prior to restriking the lamp arc. Whenever a lamp is shut down, it generally must be cooled below about 800.degree. F. before the re-starting cycle can take place. Another operational feature of such a mercury vapor lamp is that there is an average of four hours of operating life lost each time a lamp arc is restruck. Because of such problems, various types of apparatus have been designed, used and proposed to shield coated substrates from the heat of high temperature lamps whenever movement of such substrates is interrupted, which without shielding could lead to damage of the substrates or require a shut down of the lamps. The purpose of such shielding is not only to protect the substrate, particularly during periods when mechanical problems interrupt movement of the substrate, but to avoid shutting down the lamp which would then require that it go through an extended starting cycle each time the lamp arc is restruck.
Various apparatus and methods have been proposed and used for shielding moving substrates from high temperature lamp sources, such as ultra-violet lamps or infrared red lamps. Generally speaking, such apparatus and/or methods can be classified into two general categories. The first category includes hinged, pivoted or rotated shields and/or light sources. Among them would be the inventions disclosed in U.S. Pat. No. 3,745,307 to R. Nitch, entitled "Dryer for Printing Presses"; U.S. Pat. No. 2,127,956 to R. Helmer, entitled "Method and Apparatus for Drying Printing Ink"; U.S. Pat. No. 3,733,709 to R. W. Bassemir et al., entitled "Reflector and Cooling Means Therefor"; U.S. Pat. No. 3,829,982 to R. W. Pray et al., entitled "Ink Curring and Drying Apparatus"; U.S. Pat. No. 4,005,135 to N. A. Helding, entitled "Rotatable Ultra-Violet Lamp Reflector and Heat Sink"; and U.S. Pat. No. 4,494,316 to E. Stephansen et al., entitled "Apparatus for Drying a Moving Web". The second category includes sliding and reciprocating shutters. Among them would be the inventions disclosed in U.S. Pat. No. 3,826,014 to N. A. Helding, entitled "Shutter Mechanism for Radiation-Curing Lamp"; U.S. Pat. No. 3,967,385 to D. L. Culbertson, entitled "Utilization of Heat Pipes for Cooling Radiation-Curing Systems" and U.S. Pat. No. 4,037,329 to S. J. Wallace, entitled "Shutter and System Employing Same".
The methods and apparatus of the above mentioned patents and other known prior art systems for protecting coated substrates from over-heating, particularly during temporary curtailment of operations, work well initially, but the apparatus traditionally has had a relatively short mechanical life. The extreme heat generated by the ultra-violet lamps causes the shielding apparatus to buckle and warp in a manner which both interferes with its proper operation and reduces its shielding function. Many of the shielding shutters currently available utilize very light-weight metals to reduce the shutter weight in an effort to reduce the total mass of the shutter as the length of the shutter proportionally increases with the increased length of the lamps in wide presses. However, with light-weight material or any shutter material used with large presses, shutters tend to warp and sag because the overall large mass of their sheer size absorbs a large amount of heat during lamp operations.